auth2-hostbased.c

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/*
 * Copyright (c) 2000 Markus Friedl.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"
RCSID("$OpenBSD: auth2-hostbased.c,v 1.6 2004/01/19 21:25:15 markus Exp $");

#include "ssh2.h"
#include "xmalloc.h"
#include "packet.h"
#include "buffer.h"
#include "log.h"
#include "servconf.h"
#include "compat.h"
#include "bufaux.h"
#include "auth.h"
#include "key.h"
#include "canohost.h"
#include "monitor_wrap.h"
#include "pathnames.h"

/* import */
extern ServerOptions options;
extern u_char *session_id2;
extern u_int session_id2_len;

static int
userauth_hostbased(Authctxt *authctxt)
{
        Buffer b;
        Key *key = NULL;
        char *pkalg, *cuser, *chost, *service;
        u_char *pkblob, *sig;
        u_int alen, blen, slen;
        int pktype;
        int authenticated = 0;

        if (!authctxt->valid) {
                debug2("userauth_hostbased: disabled because of invalid user");
                return 0;
        }
        pkalg = packet_get_string(&alen);
        pkblob = packet_get_string(&blen);
        chost = packet_get_string(NULL);
        cuser = packet_get_string(NULL);
        sig = packet_get_string(&slen);

        debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d",
            cuser, chost, pkalg, slen);
#ifdef DEBUG_PK
        debug("signature:");
        buffer_init(&b);
        buffer_append(&b, sig, slen);
        buffer_dump(&b);
        buffer_free(&b);
#endif
        pktype = key_type_from_name(pkalg);
        if (pktype == KEY_UNSPEC) {
                /* this is perfectly legal */
                logit("userauth_hostbased: unsupported "
                    "public key algorithm: %s", pkalg);
                goto done;
        }
        key = key_from_blob(pkblob, blen);
        if (key == NULL) {
                error("userauth_hostbased: cannot decode key: %s", pkalg);
                goto done;
        }
        if (key->type != pktype) {
                error("userauth_hostbased: type mismatch for decoded key "
                    "(received %d, expected %d)", key->type, pktype);
                goto done;
        }
        service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" :
            authctxt->service;
        buffer_init(&b);
        buffer_put_string(&b, session_id2, session_id2_len);
        /* reconstruct packet */
        buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
        buffer_put_cstring(&b, authctxt->user);
        buffer_put_cstring(&b, service);
        buffer_put_cstring(&b, "hostbased");
        buffer_put_string(&b, pkalg, alen);
        buffer_put_string(&b, pkblob, blen);
        buffer_put_cstring(&b, chost);
        buffer_put_cstring(&b, cuser);
#ifdef DEBUG_PK
        buffer_dump(&b);
#endif
        /* test for allowed key and correct signature */
        authenticated = 0;
        if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) &&
            PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
                        buffer_len(&b))) == 1)
                authenticated = 1;

        buffer_free(&b);
done:
        debug2("userauth_hostbased: authenticated %d", authenticated);
        if (key != NULL)
                key_free(key);
        xfree(pkalg);
        xfree(pkblob);
        xfree(cuser);
        xfree(chost);
        xfree(sig);
        return authenticated;
}

/* return 1 if given hostkey is allowed */
int
hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost,
    Key *key)
{
        const char *resolvedname, *ipaddr, *lookup;
        HostStatus host_status;
        int len;

        resolvedname = get_canonical_hostname(options.use_dns);
        ipaddr = get_remote_ipaddr();

        debug2("userauth_hostbased: chost %s resolvedname %s ipaddr %s",
            chost, resolvedname, ipaddr);

        if (options.hostbased_uses_name_from_packet_only) {
                if (auth_rhosts2(pw, cuser, chost, chost) == 0)
                        return 0;
                lookup = chost;
        } else {
                if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
                        debug2("stripping trailing dot from chost %s", chost);
                        chost[len - 1] = '\0';
                }
                if (strcasecmp(resolvedname, chost) != 0)
                        logit("userauth_hostbased mismatch: "
                            "client sends %s, but we resolve %s to %s",
                            chost, ipaddr, resolvedname);
                if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0)
                        return 0;
                lookup = resolvedname;
        }
        debug2("userauth_hostbased: access allowed by auth_rhosts2");

        host_status = check_key_in_hostfiles(pw, key, lookup,
            _PATH_SSH_SYSTEM_HOSTFILE,
            options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);

        /* backward compat if no key has been found. */
        if (host_status == HOST_NEW)
                host_status = check_key_in_hostfiles(pw, key, lookup,
                    _PATH_SSH_SYSTEM_HOSTFILE2,
                    options.ignore_user_known_hosts ? NULL :
                    _PATH_SSH_USER_HOSTFILE2);

        return (host_status == HOST_OK);
}

Authmethod method_hostbased = {
        "hostbased",
        userauth_hostbased,
        &options.hostbased_authentication
};

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